Switching device for highfrequency circuits



E. O. WILLOUGHBY June 29, 1.948.

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SWITCHING DEVICE FOR HIGH FREQUENCY CIRCUITS Filed Sept. 9, 1942 2 Sheets-Sheet 2 Fig" 3A 1 4 M12 Jam Patented June 29, 1948 SWITCHING DEVICE FOR HIGH FREQUENCY CIRCUITS" 4 Eric Osborne Willoughby, London W. 0.2, Eng-v land, assignor to Standard Telephones and Cables Limited, London, England, a British company Application September 9, 1942, Serial No. 457,797

In Great Britain August; 11, 1941 4 y Section 1, Public Law 690, August 8, 1946 A n l Patent expires August 11, 1961 4 4 4 4 n x 2 Claims. (01. 178-44) The present invention relates to switching arrangements for use with radio frequencies and more particularly with high and ultra-high radio frequencies.

An object of the invention is to provide switching arrangements suitable for use in systems employing high and ultra-high radio frequencies for alternately allowing and preventing the energisation of an antenna or antenna system for instance in a blind approach system for aircraft and whilst the invention will be described hereinafter in connection with such a system, it will be understood that the switching arrangement according to. the invention is equally applicable to other systems involving such an operation of alternatelyswitching inancl out. I

, In the systematic switching of the lobes of the radiation or response pattern of an antenna system used for path definition in a blind approach system, the problem arises of open circuiting or blocking a transmission line during the time the antenna, or antennae connected to it are out of action, or of alternately switching in and out of a transmission line a half wavelength length of path to cause a phase change of 180 in the current to or from the antennaor antennae connected to it.

According to the invention a switching arrangement for use with radio frequencies for connecting a circuit to one or other of two transmission lines comprises rejector circuits connected in series in the respective transmission lines and means for altering the capacities of thetwo rejector circuits simultaneously in such manner that when one circuit is tuned to resonance the other is dettmed,

The invention will be better understood from the following description taken in conjunction with the accompanying drawings which show by way of example a preferred embodiment and two applications thereof, namely:

(a) A unit for alternately allowing current to pass to one antenna unit and blocking'the cur,- rent to the other antenna unit to define the approach path in a radio blind approach system.

(b) A unit for alternately switching in and out of circuit, a half wave-length length of transmission line, in series with a transmission path to produce 180 phase change in the delivered current.

Referring to the drawings,

Fig. 1 shows a preferred mechanical construction of the switch according to the invention;

Fig. 2 is a simplified circuit diagram showing the electrical equivalent circuit of the switchshown in Fig. 1; 1

Figs. 3' and 3A are explanatory diagrams; Fig. 4 shows details used in connection with the construction-shown in Fig. 1, and 4 M Fig. 5 shows a phase changing arrangement employing a switch constructed as shown in- Fig. 1.

In Fig. 1, the reference 3 indicates-a rotatable drum of which the surface-indicated by 2 is a metallic conductor theremainder of the surface indicated by I being non-conducting and: as shown, may be cut away, IV is a screening box through which pass the inner conductors 101L100 4 On rotation of the drum the lines OP and OR" alternately become blocked to the operating current, and in the position shown in Figure l thev path OR is conducting while the pathQPf is blocked, this result being due to the factthat path OP' is in a parallel tuned rejector circuit when faced bya non-conducting portion I of the drum and capacity in parallel with OR representing a pass capacityapproximately equal to the series capacity of the two capacities from R to.2 and Q- to 2. Similarly when the drum is rotated through an angle so that the metallic part 2 is brought opposite toplate P then path OP is conducting and OR is blocked.

-If another transmission line A is introduced through the screening case 1 and, its innerconductor 10a is connected to the conductor BC at 0, power may be alternately passed through A03 and AOC on rotation of thedrum 2, and if the conducting plates 2 are so proportioned OP can be arranged to pass. current for a dot interval and ORFfor a dash-interval or vice versa.

An external source of power such as an electric motor can be connected to shaft l2 for rotating the switchdrum 3. 4 4 4 Referring to Figure 1 line A may be regarded as the transmission line to the translation circuit, and-B and C the transmission lines to thetwo antenna units of a radio, blind approach system. 4 4 4i be the transmission line to the translation circult, and either B or C may be selected as the transmission line to an antenna unit the phase of whose current is to be varied 180 by the switch and then R and P are connected by a length of transmission line equivalent to the desired phase shift or with an integral number of wave The.

readily achieved in practice, and is not, even a strictly true representation of Figure 1.

A much more accurate representation of the operation of the switch is shown in Figure 3 which can be shown to be equivalent to two 1r networks the inductive branch of which in the blockedcircuit is parallel tuned and permits no current to pass, and for the pass circuit and bridging efiect of the drum is equivalent to adding a pass capacity CP (Fig. 3A), and makes as a pass circuit an equivalent 1r network of capacities Ce, CP, CR, as shown in Figure 3A.

Hence the need of the system of controls shown in" Figure 4 becomes evident, and has the advantage of taking into account to' a large extent mechanical inaccuracies, such as unequal gaps between pole pieces P and R and the drum.

The matching stubs SI, S2, S3 enable the pass 1r-networks to have their shunt legs tuned to be inductive and the correct value to match the characteristic impedances of input and output lines with a pass capacity of Cr.

In order to tune each rejector circuit to the operating frequency short lengths of transmission line with a slide attachment for varying the length in circuit are inserted in the lengths of transmission line P'O and RO as shown at M, N in Figure 4. These short lengths M, N represent variable inductances to tune the stray capacity produced by stubs PP and Q0 or RR and Q0 (Figure 1) with the non-conducting pornon of the drum when opposite P or R.

Alternatively the'rejector circuit may comprise small inductance coils and trimming condensers in place of conductors OP, OR each rejector circuit being trimmed when the plate P or Q is faced by a non-conducting portion of the rotating drum, the final tuning of the rejector circuit to the operating frequency being carried out by'the trimming condenser, which is preferably small in order to keep the reactances in parallel across the points P and O and O and R as high as possible-thus keeping the rejection resistance very high.

In regard to other adjustments such as may be required to match transmission lines to the antenna units, these are standard practice to those versed in the art, and will not be further discussedthey form part of the adjustment of the circuits whatever type of 'R.'F. switch is used.

Any known method of forming a rejector circuit between P and O, and between 0 and R which can be changed to a fixed reactance on the rotation of a drum or metal sectors may be used.

Itwill be understood that the switch could be adjusted in the reverse manner to that described namely, to pass when the stubs and fixed P, Q, R plates are faced by conducting metal 2, but this is not so good a block as it implies, the mechanical work is perfect giving fixed capacity P2 plus 2-Q in series and Q2 plus 2R in series throughout the blocking period, and as small variations in the pass reactance are not of practical importance, it will be realised the preferred method of operation and adjustment is superior where mechanical accuracy of the rotating condenser is not relied upon to give a good blocking effect.

Advantages of the type of switch described are:

(a) The adjustments are independent The conditions for a block on the two alternative sides of the drum are first adjusted, and then the matching stubs are independently altered to give full power on alternative feeder lines, dealing with one side of the switch at a time.

(b) Highly accurate mechanical construction is not essential The matching and tuning adjustments provided take up all centering errors of the drum and stationaryplates P, Q, R and a good block of the unwanted lines is not dependent on mechanical accuracy.

The only error not taken up is that due to the. mechanical axle of the drum not being its true axis and this is easy to avoid by turning up the surface of the drum on its own axle as axis.

(0) Operation with modulation Provided a reasonable L/C ratio of the parallel tuned circuit is used a modulated wave may be satisfactorily switched, when the band width is narrow enough to keep the blocking impedance at the extreme frequencies 8-10 times the characteristic impedance of the lines.

(4d) Will operate anywhere in wide frequency band By readjustment of the tuning controls, and matching controls the switch may be operated at any frequency in a wide frequency range and can be matched into different impedance transmission lines.

Although the invention has been described in its application to a concentric conductor transmission line, it is equally applicable to open wire transmission lines, as will be clear to those skilled in the art. Networks which are alternately rendered in the .block and pass condition are connected in series with either one or both lines and they may be adjusted and matched by methods analogous to those described for the concentric conductor transmission line.

What is claimed is:

1. Switch arrangements for use with radio frequencies for connecting a main coaxial transmission line to one or other of two branch coaxial transmission lines comprising parallel resonant rejector circuits connected in series in the respective branch lines, condensers for tuning said rejector circuits alternately comprising a rotatable drum provided with two series of conducting and non-conducting portions arranged alternately around the circumference of the drum, and located at difierent points along the axis to cooperate with fixed condenser plates connected to the terminals of the respective rejector circuits notin common thereto, said series of conducting portions being in electrical communication with a further conducting plate arranged to cooperate with a fixed plate connected to a point on said main line, the inductance of each said rejector circuit comprising a length of the central conductor of the coaxial line forming the respective branch line, each such length of central conductor having an adjustable loop in series therewith to vary independently the inductance of the respective circuits and to adapt the arrangements for use with different frequencies or to compensate for irregularities in the use of mechanically variable condensers.

2. A switching apparatus for use with circuits at high frequencies comprising a metallic casing having a generally rectangular shape, a coaxial line having a central conductor passing through a central region in one casing wall with the outer conductor grounded to said casing, said central conductor extending normal to said casing wall inwardly within said casing for a length and terminating in a condenser plate, two branch coaxial lines each having a central conductor passing through the opposed parallel sides of said casing, said parallel sides being perpendicular to the firstnamed wall, said two coaxial cables having the outer conductors grounded to said casing and having their inner conductors extending ,perpendicular to the inner conductor of the first coaxial cable and connected thereto, metallic conductors extending from the branch inner conductors, a condenser plate terminating each such metallic conductor, said three condenser plates being aligned along an axis parallel to the branch central conductors, a drive shaft journaled in said parallel walls of said casing through which said branch conductors pass, a metallic cylindrical drum carried by said drive shaft, said drum having a continuous metallic conducting surface at the center thereof and having alternate conducting and non-conducting portions circumferentially thereof at the ends, the conducting and nonconducting area at one end being angularly staggered with respect to the other end, said drum and condenser plates being so arranged that, as said drum is turned, the center condenser plate always has drum metal opposed thereto for condenser action and one end condenser plate at a time has drum metal opposed thereto, said entire system within the casing being so proportioned and adjusted that the branch center conductors have an inductive reactance and the condenser plates and supports form capacitive branches so that a parallel resonant circuit in series between the main coaxial conductor and each branch may be provided.

ERIC OSBORNE WILLO'UGHBY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,005,798 Moser June 25, 1935 2,189,549 Hershberger Feb. 6, 1940 2,198,025 Davies et a1 Apr. 23, 1940 2,204,175 Carter June 11, 1940 2,207,039 Alford July 9, 1940 2,228,692 Davies Jan. 14, 1941 2,232,592 Davies Feb. 18, 1941 2,235,010 Chaffee M Mar. 18, 1941 2,285,851 Byrne June 9, 1942 2,294,103 Von Ottenthal Aug. 25, 1942 FOREIGN PATENTS Number Country Date 114,047 Australia Oct. 14, 1941 

